This application is related to U.S. patent application Ser. No. 09/399,752, also entitled xe2x80x9cFiber Retaining Systemxe2x80x9d, filed simultaneously herewith, and which is hereby incorporated by reference.
The present invention relates to the retention and protection of loose spliced optical fibers. More specifically, the invention relates to a housing for containing and protecting a fiber optic splice and a portion of the optical fibers on opposite sides leading to the splice.
Communications networks are frequently made of many miles of optical fibers. Indeed, many of the networks can extend between continents and across oceans and other large bodies of water. For protection, the optical fibers are contained in a larger cable. An example of such a prior art cable is shown in FIG. 1. The cable 2 includes an outer insulating plastic coating 4, a copper sheath 6 inside the outer coating 4, and high strength members, such as steel wires 8, inside of the copper sheath 6. A loose tube 10 is contained within the steel wires 8, and one or more isolated optical fibers 12 are contained within the loose tube 10. This permits the fibers 12 to move with respect to the steel wires 8, the sheath 6 and the coating 4. This cable arrangement has been found to be desirable in many high strength applications.
As neither the cables nor the fibers can be made and deployed in infinite lengths, sections of the cables and the fibers are attached together. The fibers are typically attached to each other by a process known as splicing. For protection from the environment, these spliced sections are commonly contained in a watertight housing, which is frequently referred to as a joint box. Such housings or joint boxes are also used when it is necessary to make splices in the field. In circumstances when tension is applied to the cable, such as during the deployment of the cable underwater by a ship, it is undesirable to have the splice absorb the applied tension forces or to have the spliced portion leave the joint box and go back inside the cable.
In a prior joint box design, the end portions of which are disclosed in U.S. Pat. No. 4,507,008, the high strength steel wires are clamped to a first end of a joint box between a socket body and a plug and sleeve arrangement. The plug and sleeve are hollow along their central axis and the fibers extend unrestrained therethrough. A similar arrangement exists at the other end of the joint box. A center section or shelf of the joint box extends between the cable termination end sections. The fibers are provided with a great deal of slack, such as three feet of fibers, and the ends of the fibers are fused. The joined fibers, with their slack, are coiled onto the center section. The splice itself is fixed within the center section. The large amount of slack is intended to enable the fused optical fiber to be pulled or tensioned without placing stress on the splice and without the splice being pulled into one of the cables.
However, a large amount of excess slack may be undesirable from an assembly standpoint. Further, when the excess slack is bent to fit within the housing, the fibers could become damaged. Additionally, in this arrangement, affixing the splice directly within the housing can also be undesirable because if the slack is removed, the stresses and strains are applied at the splice. Accordingly, a solution that overcomes the drawbacks of the prior art was needed.
In view of the foregoing, it is a principal object of the present invention to provide an arrangement for restraining and protecting spliced optical fibers in a joint box.
It is another object of the present invention to provide a housing or joint box that eliminates the large amount of slack of optical fiber that needs to be used inside.
It is yet another object of the present invention to immobilize the optical fibers inside a joint box at a position spaced from the splice so that forces applied to the optical fibers are isolated from the spliced section.
It is another object of the present invention to prevent the optical fibers inside the joint box from moving in and out of their cables.
These and other objects are achieved in accordance with the present invention by an apparatus having first and second cables, each having a strengthening portion and an optical fiber positioned inside of the strengthening portion. In each cable, each optical fiber is axially movable with respect to its respective strengthening portion and has a terminal end. The terminal ends of the optical fibers are spliced together at a splice location to form a continuous optical fiber. A housing includes opposed longitudinal end portions that are coupled to the strengthening portion of a respective cable. A fiber restraining device is spaced from the splice location and restrains the movement of the continuous optical fiber. The fiber restraining device may be a friction imparting element having a curved outer surface. An optical fiber is tensioned around the curved outer surface of the friction imparting element.
In another object, the present invention includes an apparatus having first and second cables, each having a strengthening portion and an optical fiber positioned inside of the strengthening portion. The optical fiber has a minimum bend radius at which the fiber will fail to reliably send optical signals thereon. The optical fiber is longitudinally movable with respect to its respective strengthening portion and has a terminal end. The terminal ends of the optical fibers are spliced together at a splice location to form a continuous optical fiber. A housing includes opposed longitudinal end portions and the strengthening portion of each cable is coupled to a respective end portion. The housing includes a friction imparting element having a curved convex surface having a radius of curvature not less than the minimum bend radius. The optical fiber is tensioned around the curved convex surface.
In an alternative object, the present invention includes an apparatus having first and second cables, each having a strengthening portion and an optical fiber positioned inside of the strengthening portion. In each cable, the optical fiber is longitudinally movable with respect to its respective strengthening portion and has a terminal end. The terminal ends of the optical fibers are spliced together at a splice location to form a continuous optical fiber. The housing includes opposed longitudinal end portions and a longitudinally extending divider separating the housing into first and second compartments. The housing is coupled to the strengthening portion of each cable. The housing further including first and second fiber restraining devices located in different compartments for restraining different portions of the continuous optical fiber.
In another object, the present invention includes an apparatus having first and second end portions, each having a cable attachment device. A fiber splicing region is disposed between the first and second end portions and can hold a spliced segment of a spliced fiber. First and second fiber retaining devices each include a drum having a curved outer surface adapted to impart friction to an optical fiber wound thereon. A fiber holdback device includes a concave surface that is substantially complimentary shaped to the curved outer surface. The fiber holdback device is positioned adjacent to a portion of the curved outer surface.
The above and other objects, features and advantages of the present invention will be readily apparent and fully understood from the following detailed description of preferred embodiments, taken in connection with the appended drawings.